Formation of MAX solid solutions (Ti,V)2AlC and (Cr,V)2AlC with Al2O3 addition by SHS involving aluminothermic reduction

Abstract MAX solid solutions (Ti,V) 2 AlC and (Cr,V) 2 AlC with Al 2 O 3 addition were produced by solid state combustion involving aluminothermic reduction in the mode of self-propagating high-temperature synthesis (SHS). Starting materials included TiO 2 /V 2 O 5 /Al/Al 4 C 3 and Cr 2 O 3 /V 2 O 5 /Al/Al 4 C 3 powder mixtures. Attempts were made to attain (Ti 1− x V x ) 2 AlC and (Cr 1− y V y ) 2 AlC with the V content in terms of x and y from 0.1 to 0.7. Combustion exothermicity was increased by increasing V 2 O 5 for the yield of a higher proportion of V at the substitution site, which not only increased the combustion temperature and reaction front velocity, but also facilitated the evolution of solid solutions. Due to insufficient reaction exothermicity, (Ti 1− x V x ) 2 AlC/Al 2 O 3 in situ composites were only produced under x ≥0.4. On the other hand, the formation of (Cr 1− y V y ) 2 AlC/Al 2 O 3 was achieved with y from 0.1 to 0.7, because reduction of Cr 2 O 3 is more energetic than that of TiO 2 . The laminated microstructure characteristic of the MAX ternary carbide was observed for both Al 2 O 3 -added (Ti,V) 2 AlC and (Cr,V) 2 AlC composites synthesized in this study.